Motorcycle engines typically have either overhead cam or push rod valve operation. With push rod valve operation, the push rods typically operate rocker assemblies, each having a rocker mounted to a rocker support. The rocker assemblies are positioned within a rocker box mounted above a cylinder assembly (i.e., a cylinder and cylinder head). The rocker box includes a lower section that is formed integrally with the rocker supports, and an upper section that completes the enclosure for the rocker assemblies.
When the engine is mounted in the frame of some motorcycles, the rocker box is positioned very close to one of the frame members. Such close proximity requires that the entire engine be removed from the frame in order to remove the upper section of the rocker box to have access to the rocker assemblies. In this regard, it is known to produce the upper section of the rocker box in two portions: a middle portion and an upper portion. Because each of the two portions is thinner than the one-piece upper section, they can be removed from the engine one at a time while the engine is mounted in the frame.